FIG. 12 shows a conventional waveguide connecting structure. As illustrated, two hollow waveguides 100 and 200 to be connected together include flanges 101 and 201 at the connecting ends thereof, respectively. The connection can be made by aligning openings 102 and 202 of the waveguides 100 and 200 through which an electromagnetic wave are propagated, and then, pressing one of the waveguides 100 (or 200) against the other waveguide 200 (or 100) to join the flanges 101 and 201 together along a direction designated by the arrows.
In this construction, it is difficult to achieve high flatness (including surface roughness, surface irregularity, parallelism, etc.) throughout the flange surfaces, there may be a high number of gaps between the flanges. Thus, a leakage of an electromagnetic wave may occur from the gaps.
It is difficult to process the flanges with high flatness at low cost. Therefore, to address the leakage, for example, instead of depending only on the flatness of the flanges, Japanese Unexamined Patent Application Publication No. 2007-5955 discloses a deformable projection formed around an opening of one of the flanges. The projection can be plastically deformed when the flanges are pressed together so that the deformed projection fills the gaps to prevent the leakage.
However, in the above construction, the pressure of the flanges must be properly controlled and, thus, the flanges may be required to be bolted together to achieve the proper pressure. Furthermore, if the flanges cannot be bolted together for some reason (i.e., the space around the flanges is limited), a proper pressure cannot be applied to the flanges. Moreover, the bolt construction makes it difficult to disassemble the flange connection for maintenance and replacement of the components.